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1 .TH PCRE 3 "11 November 2012" "PCRE 8.32"
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 The PCRE library is a set of functions that implement regular expression
8 pattern matching using the same syntax and semantics as Perl, with just a few
9 differences. Some features that appeared in Python and PCRE before they
10 appeared in Perl are also available using the Python syntax, there is some
11 support for one or two .NET and Oniguruma syntax items, and there is an option
12 for requesting some minor changes that give better JavaScript compatibility.
13 .P
14 Starting with release 8.30, it is possible to compile two separate PCRE
15 libraries: the original, which supports 8-bit character strings (including
16 UTF-8 strings), and a second library that supports 16-bit character strings
17 (including UTF-16 strings). The build process allows either one or both to be
18 built. The majority of the work to make this possible was done by Zoltan
19 Herczeg.
20 .P
21 Starting with release 8.32 it is possible to compile a third separate PCRE
22 library, which supports 32-bit character strings (including
23 UTF-32 strings). The build process allows any set of the 8-, 16- and 32-bit
24 libraries. The work to make this possible was done by Christian Persch.
25 .P
26 The three libraries contain identical sets of functions, except that the names
27 in the 16-bit library start with \fBpcre16_\fP instead of \fBpcre_\fP, and the
28 names in the 32-bit library start with \fBpcre32_\fP instead of \fBpcre_\fP. To
29 avoid over-complication and reduce the documentation maintenance load, most of
30 the documentation describes the 8-bit library, with the differences for the
31 16-bit and 32-bit libraries described separately in the
32 .\" HREF
33 \fBpcre16\fP
34 and
35 .\" HREF
36 \fBpcre32\fP
37 .\"
38 pages. References to functions or structures of the form \fIpcre[16|32]_xxx\fP
39 should be read as meaning "\fIpcre_xxx\fP when using the 8-bit library,
40 \fIpcre16_xxx\fP when using the 16-bit library, or \fIpcre32_xxx\fP when using
41 the 32-bit library".
42 .P
43 The current implementation of PCRE corresponds approximately with Perl 5.12,
44 including support for UTF-8/16/32 encoded strings and Unicode general category
45 properties. However, UTF-8/16/32 and Unicode support has to be explicitly
46 enabled; it is not the default. The Unicode tables correspond to Unicode
47 release 6.2.0.
48 .P
49 In addition to the Perl-compatible matching function, PCRE contains an
50 alternative function that matches the same compiled patterns in a different
51 way. In certain circumstances, the alternative function has some advantages.
52 For a discussion of the two matching algorithms, see the
53 .\" HREF
54 \fBpcrematching\fP
55 .\"
56 page.
57 .P
58 PCRE is written in C and released as a C library. A number of people have
59 written wrappers and interfaces of various kinds. In particular, Google Inc.
60 have provided a comprehensive C++ wrapper for the 8-bit library. This is now
61 included as part of the PCRE distribution. The
62 .\" HREF
63 \fBpcrecpp\fP
64 .\"
65 page has details of this interface. Other people's contributions can be found
66 in the \fIContrib\fP directory at the primary FTP site, which is:
67 .sp
68 .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
69 .\" </a>
70 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
71 .P
72 Details of exactly which Perl regular expression features are and are not
73 supported by PCRE are given in separate documents. See the
74 .\" HREF
75 \fBpcrepattern\fP
76 .\"
77 and
78 .\" HREF
79 \fBpcrecompat\fP
80 .\"
81 pages. There is a syntax summary in the
82 .\" HREF
83 \fBpcresyntax\fP
84 .\"
85 page.
86 .P
87 Some features of PCRE can be included, excluded, or changed when the library is
88 built. The
89 .\" HREF
90 \fBpcre_config()\fP
91 .\"
92 function makes it possible for a client to discover which features are
93 available. The features themselves are described in the
94 .\" HREF
95 \fBpcrebuild\fP
96 .\"
97 page. Documentation about building PCRE for various operating systems can be
98 found in the \fBREADME\fP and \fBNON-AUTOTOOLS_BUILD\fP files in the source
99 distribution.
100 .P
101 The libraries contains a number of undocumented internal functions and data
102 tables that are used by more than one of the exported external functions, but
103 which are not intended for use by external callers. Their names all begin with
104 "_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
105 clashes. In some environments, it is possible to control which external symbols
106 are exported when a shared library is built, and in these cases the
107 undocumented symbols are not exported.
108 .
109 .
111 .rs
112 .sp
113 If you are using PCRE in a non-UTF application that permits users to supply
114 arbitrary patterns for compilation, you should be aware of a feature that
115 allows users to turn on UTF support from within a pattern, provided that PCRE
116 was built with UTF support. For example, an 8-bit pattern that begins with
117 "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
118 subjects as strings of UTF-8 characters instead of individual 8-bit characters.
119 This causes both the pattern and any data against which it is matched to be
120 checked for UTF-8 validity. If the data string is very long, such a check might
121 use sufficiently many resources as to cause your application to lose
122 performance.
123 .P
124 The best way of guarding against this possibility is to use the
125 \fBpcre_fullinfo()\fP function to check the compiled pattern's options for UTF.
126 .P
127 If your application is one that supports UTF, be aware that validity checking
128 can take time. If the same data string is to be matched many times, you can use
129 the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
130 save redundant checks.
131 .P
132 Another way that performance can be hit is by running a pattern that has a very
133 large search tree against a string that will never match. Nested unlimited
134 repeats in a pattern are a common example. PCRE provides some protection
135 against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
136 .\" HREF
137 \fBpcreapi\fP
138 .\"
139 page.
140 .
141 .
143 .rs
144 .sp
145 The user documentation for PCRE comprises a number of different sections. In
146 the "man" format, each of these is a separate "man page". In the HTML format,
147 each is a separate page, linked from the index page. In the plain text format,
148 all the sections, except the \fBpcredemo\fP section, are concatenated, for ease
149 of searching. The sections are as follows:
150 .sp
151 pcre this document
152 pcre16 details of the 16-bit library
153 pcre32 details of the 32-bit library
154 pcre-config show PCRE installation configuration information
155 pcreapi details of PCRE's native C API
156 pcrebuild options for building PCRE
157 pcrecallout details of the callout feature
158 pcrecompat discussion of Perl compatibility
159 pcrecpp details of the C++ wrapper for the 8-bit library
160 pcredemo a demonstration C program that uses PCRE
161 pcregrep description of the \fBpcregrep\fP command (8-bit only)
162 pcrejit discussion of the just-in-time optimization support
163 pcrelimits details of size and other limits
164 pcrematching discussion of the two matching algorithms
165 pcrepartial details of the partial matching facility
166 .\" JOIN
167 pcrepattern syntax and semantics of supported
168 regular expressions
169 pcreperform discussion of performance issues
170 pcreposix the POSIX-compatible C API for the 8-bit library
171 pcreprecompile details of saving and re-using precompiled patterns
172 pcresample discussion of the pcredemo program
173 pcrestack discussion of stack usage
174 pcresyntax quick syntax reference
175 pcretest description of the \fBpcretest\fP testing command
176 pcreunicode discussion of Unicode and UTF-8/16/32 support
177 .sp
178 In addition, in the "man" and HTML formats, there is a short page for each
179 C library function, listing its arguments and results.
180 .
181 .
183 .rs
184 .sp
185 .nf
186 Philip Hazel
187 University Computing Service
188 Cambridge CB2 3QH, England.
189 .fi
190 .P
191 Putting an actual email address here seems to have been a spam magnet, so I've
192 taken it away. If you want to email me, use my two initials, followed by the
193 two digits 10, at the domain cam.ac.uk.
194 .
195 .
197 .rs
198 .sp
199 .nf
200 Last updated: 11 November 2012
201 Copyright (c) 1997-2012 University of Cambridge.
202 .fi


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